The present disclosure relates to power supply control systems, and specifically to power supply control in an electronic apparatus including a power supply device, and a semiconductor integrated circuit which operates based on an output voltage of the power supply device.
FIG. 22 illustrates an application circuit described in LM5005—High Voltage 2.5 Amp Buck Regulator, Datasheet, [online], National Semiconductor, March 2006, [retrieved on 2011 Apr. 28], Retrieved from the Internet: <URL: http://www.alldatasheet.com/datasheet-pdf/pdf/180844/NSC/LM5005.html>. In this power supply system, a smoothing coil 2203, a smoothing capacitor 2204, and a resistive voltage divider circuit 2205 which are mounted on substrates are connected to a power supply output terminal 2202 of a power supply IC 2201. Moreover, a power supply terminal 2208 of a system-on-a-chip (SoC) section 2207 is connected to a node 2206 to which the resistive voltage divider circuit 2205 is connected, thereby supplying a power supply voltage to the SoC section 2207. The power supply IC 2201 mainly composed of analog circuits generates an output voltage of a magnitude in accordance with a voltage VFB obtained by dividing an output voltage by the resistive voltage divider circuit 2205, and the SoC section 2207 operates in response to the output voltage as the power supply voltage received as a reference. In this type of electronic apparatus, the resistive voltage divider circuit 2205 includes a fixed resistor, and the divided voltage ratio is fixed, so that it is not possible to dynamically control a set output voltage. Moreover, accuracy of the power supply voltage is ensured only when the resistive voltage divider circuit 2205 is disposed in the immediate vicinity of the power supply IC 2201, and the power supply voltage is measured at the node 2206 near the power supply IC 2201. Thus, impedance of a power supply interconnect extending from the power supply IC 2201 to the SoC section 2207 or accuracy of components such as a resistive element of the resistive voltage divider circuit 2205 may cause variations in the power supply voltage of the SoC section 2207. As a result, the performance of the SoC section 2207 significantly depends on accuracy of the power supply potential of the power supply system. Thus, there has been demand to dynamically and accurately control the power supply voltage of the SoC section 2207 in accordance with the accuracy of the components and the impedance of the power supply interconnect.
FIG. 23 illustrates a configuration of a system described in LP5552—PWI 2.0 and PowerWise Technology Compliant Energy Management Unit, Datasheet, [online], National Semiconductor, May 20, 2008, [retrieved on 2011 Apr. 28], Retrieved from the Internet: <URL: http://www.alldatasheetnet/datasheet-pdf/pdf/239791/NSC/LP5552.html>. This power supply system has a configuration as an electronic apparatus capable of dynamically and accurately controlling a power supply voltage. A power supply IC 2301 has a power management (PM) function by which the power supply voltage can be dynamically controlled. Moreover, a SoC section 2302 includes a performance monitor circuit (HPM) 2303 configured to monitor characteristics such as circuit delay. The power supply IC 2301 for PM includes a digital control circuit 2305 in which a digital feedback signal 2304 output from the SoC section 2302 is digitally processed. A signal 2306 obtained after the digital processing in the digital control circuit 2305 is converted to an analog signal 2307 by a built-in D/A converter (DAC) circuit, and is controlled so that an output voltage 2308 is a voltage according to demanded performance of the SoC section 2302. Based on a result of the monitoring by the performance monitor circuit 2303, the SoC section 2302 determines a voltage value necessary for normal circuit operation of the SoC section 2302, and outputs the voltage value as the digital feedback signal 2304 to the power supply IC 2301 for the PM. With this power supply system, the output voltage 2308 can be controlled so that Vdd is in the range from about 0.6 V to about 1.2 V.
Japanese Patent Publication No. 2007-201455 proposes that a digital signal processing operation of a power supply voltage and a substrate voltage which minimize power of a power supply circuit (regulator) and a SoC section is performed, and a resistance value in a resistive voltage divider circuit of the regulator is changed to vary a reference voltage so that the power supply voltage has a desired power supply voltage value, thereby reducing power of a system.